FRIDAY, July 26, 2019 (HealthDay News) -- The United States has grown a bumper crop of couch potatoes in recent years, a new study reports.

The amount of time people spend sitting around actually increased after the initial release of the federal Physical Activity Guidelines for Americans in 2008, researchers have found.

"Over the past 10 years, there was no significant change in physical activity levels, but there was a significant increase in the time we sit around," said senior researcher Dr. Wei Bao. He's an assistant professor of epidemiology at the University of Iowa in Iowa City.

As a result, the proportion of people who didn't get enough aerobic exercise and also sat around for more than 6 hours a day rose from 16% to nearly 19% between 2007 and 2016, according to the study published online July 26 in JAMA Network Open.

Because of this, federal health officials released the activity guidelines, which recommend adults get at least 150 minutes a week of moderate-intensity exercise or 75 minutes a week of vigorous-intensity exercise.

Moderate-intensity activity can include mowing the lawn, playing tennis, enjoying a leisurely bike ride, engaging in a brisk walk, or doing heavy housework like vacuuming, mopping or washing windows.

To see how many Americans meet these recommendations, Bao's team reviewed data from a series of federal studies that track health trends among U.S. adults and children.

The investigators found that time spent sitting increased from 5.7 hours a day in 2007-2008 to 6.4 hours a day in 2015-2016.

The increase in sedentary behavior was seen in nearly every major subgroup of the U.S. population, the study authors said.

At the same time, there was no real change in Americans' physical activity. About 65% of people met guidelines for aerobic activity in 2015-2016, compared with 63% in 2007-2008, the study found.

American life is designed to be cushy, so it's natural that folks settle in and relax rather than get up and go, Bao said.

"This will be a natural phenomenon for a convenience society, for a modern society like the United States," he said. "I think sitting down is a natural desire for humans. When people are tired at work and go home, the first thing is to lie down on the sofa and watch TV for another two hours."

American jobs have also gotten less physically demanding, said Donna Arnett, dean of the University of Kentucky College of Public Health, in Lexington.

"If you look at physical activity from occupational energy expenditure, that has been going down dramatically over the past three to four decades," she said. "Our jobs are getting more automated. There's much less physical activity at work."

The proliferation of screens at work and home hasn't helped, she added.

"The automation in our lives -- at home and at work -- is also likely related to the increased use of screen time. People are spending more time looking at their phones and working on their computers, even after hours," Arnett said.

So why haven't the Physical Activity Guidelines been more inspiring?

It could be that folks simply don't know about them.

Only about one in three Americans said they were aware of the guidelines in a 2009 survey, and fewer than 1% could say what the guidelines recommend, researchers said in background notes.

Bao suggested that "there should be more effort to communicate this information and to have people fight against sitting down."

Smart technology also might help, Arnett said. Devices like Fitbits and Apple Watches can be programmed to regularly remind wearers to get up and move around.

Clever outreach could be key, too. Arnett said someone told her that while binge-watching Netflix, an ad from the American Heart Association appeared urging the viewer to take a break, get up and move around.

SOURCES: Wei Bao, M.D., Ph.D., assistant professor of epidemiology, College of Public Health, University of Iowa, Iowa City; Donna Arnett, Ph.D., dean, College of Public Health, University of Kentucky, Lexington; July 26, 2019, JAMA Network Open, online

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SOURCES: Wei Bao, M.D., Ph.D., assistant professor of epidemiology, College of Public Health, University of Iowa, Iowa City; Donna Arnett, Ph.D., dean, College of Public Health, University of Kentucky, Lexington; July 26, 2019, JAMA Network Open, online